The measurement of structures on wafers in the semiconductor industry is conducted pursuant to two different methods which are carried out sequentially.
The transverse measurements of structures such as the widths of conductor paths are determined by means of photometric measurements of the intensity distribution in the object plane on so-called microdensitometers. These microdensitometers are described, for example, in the publication entitled "Leitz-Mitteilungen for Wissenschaft und Technik", Volume 8, No. 3/4, pages 76 to 81. A description of these devices is also provided by U.S. Pat. No. 4,373,817. These devices are derived from microscope photometers and have a displaceable measuring slit of a few .mu.m width and are mounted in the intermediate image plane. A photomultiplier is connected in cascade with these devices. The slit is moved in the intermediate plane for scanning the intensity distribution in the object plane with a required resolution of typically 10 to 100 nm. This affords the advantage with respect to scanning directly in the object plane of less precise requirements for guidings, temperature consistency et cetera since the object structures are imaged in the intermediate plane so as to be enlarged by the scale factor of the objective.
The thicknesses of layers of the structures are mostly determined on microspectral photometers by measuring the distance of interference minima and interference maxima in the spectrum of the light reflected from the object. Microspectral photometers for the semiconductor industry are described in U.S. Pat. No. 4,087,685.
As mentioned, the investigation of wafers, for example, in the semiconductor industry requires two different apparatus each with its own means for inserting the specimen and with its own computer evaluation and the like. The wafer to be investigated must be brought to each of the two apparatus with its cassette and be positioned anew under the microscope. This requires a relatively large expenditure of time and increases the space required and the danger of contamination of the wafer to be investigated.
Even though both types of apparatus include a microscope as part of their basic structure, it is not easily possible to combine the above-mentioned apparatus. This situation is present because the additional insertion of a spectrometer is made difficult by the slit component group movably mounted in the intermediate image in microdensitometers. On the other hand, the resolution of scanning tables, which are used for positioning measuring spots of the microspectral photometers, does not satisfy the requirements for the resolution of the scanning movement associated with the microdensitometry.